The main goal of this research is to compare the various optimization strategies (Response Surface Methodology, Taguchi, and Teaching Learning Based Optimization) for orthogonal turning of Hard to Machine materials. The workpiece material in this work is Ti6Al4V alloys. After selecting cutting speeds in the High-Speed Machining range, orthogonal turning tests are performed on the material for a specific combination of machining parameters – Depth of Cut, Cutting Speed, and, Feed Rate. A Lathe Tool Dynamometer is used to record the cutting forces from the trials. After combining Johnson Cook Material and Damage models, a comprehensive Finite Element Model is created to model the Orthogonal Turning of Ti6Al4V alloys. Experiments conducted previously validate the developed model. Three different strategies, namely RSM, Taguchi, and TLBO, were used to optimise machining parameters for minimal Cutting Force. The approaches are compared for the best combination of machining parameters and the best Cutting Force value. Analysis of Variance is used to study the impact of machining factors on Cutting Force.

A review of some recent data from multiaxial fatigue data from different notched materials is carried out in the paper. The approach based on the strain energy density (SED) averaged over a control volume is first used to summarise uniaxial and multiaxial fatigue strength data of welded joints made of structural steel and aluminium alloys. In all welded joints, the weld toe and weld root regions are modelled like sharp, zero radius, V-notches with different opening angles. The control volume radius is 0.28 mm for structural steels, 0.12 mm for aluminium alloys. Afterwards the SED approach is applied to multi-axial fatigue data from plain and V-notched specimens made of AISI 416 stainless steel (hardened and tempered state), subjected to tension, torsion and combined tension and torsion, both in-phase and out-of-phase. Notched specimens are characterised by a very small root radius, ρ=0.1 mm, which results in high nonlinear effects ahead of the notch tips. All results are summarised in terms of Δ W-N (SED range versus cycles to failure) scatterbands. Together with the new results, a number of multi-axial fatigue data recently obtained from sharply notched specimens made of C40 steel (normalised state) and 39NiCrMo3 steel (hardened and tempered state) are represented with the aim to provide a global synthesis in terms of local SED. Finally a synthesis from Ti6Al4V alloy is carried out showing the capability of the SED approach to be applied also to light alloys.